Sign In to App Store Issue

I bought a used mac mini last year. I should have wiped the drive and started fresh but I didn’t. Just changed admin names and passwords. Tonight I upgraded to Yosemite. After restart and using my iCloud login and p/w all is well to proceed with updating various apps. One in particular is iPhoto. In the task bar it has the circle with the line through it. So I attempt to update it. It will not allow me to. The pop box appears asking for apple ID and password. Because I never wiped the drive. There is someone else’s email in place and greyed out. Locked in place. I was able to update all 4 apps except that one. Am I going to have to wipe the drive anyway? I also can’t seem to change the “home” name of the previous owner. I have removed them and I am Admin. Trying to find a solution for 4 hours now.

Welcome to Mac-Forums..

Your first instinct of wiping the HD and doing a fresh install was correct and the fact that the previous owner didn't do that and perhaps left their data on there is just scary.

You should now, however, go through that process and start out fresh and configure the Mac Mini like the way you want it using ONLY your credentials..

Thank you for your time and response. Have a great weekend!